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Message started by stuartross109 on 05/24/07 at 11:19:59

Title: Engine Missfire at High Revs
Post by stuartross109 on 05/24/07 at 11:19:59

Hi out there

Can you help I have a 1986 Savage that has developed a missfire at full throttle openings. It only occurs at full throttle and goes if I back off the throttle. The missfire has a regular popp, popp popp!

I have cleaned out the carb but this makes no difference. Any help please?

Title: Re: Engine Missfire at High Revs
Post by LANCER on 05/24/07 at 12:33:11

Is the alternator getting weak, and for now is only showing up at the high power end where the most stress to the ignition system is made?

Title: Re: Engine Missfire at High Revs
Post by justin_o_guy on 05/24/07 at 17:24:29

Can this be spark plug related? Sure would be easy to look into & cheap t fix.They can start to break down at higher rpm, right?

Title: Re: Engine Missfire at High Revs
Post by bduff on 05/24/07 at 18:35:21

I would start with a new spark plug

Title: Re: Engine Missfire at High Revs
Post by clueless on 05/24/07 at 19:38:46

I would check all the electrical connections, starting at the battery.

Title: Re: Engine Missfire at High Revs
Post by tx650 on 05/24/07 at 22:02:08

Had same problem with my 88. Ran a jumper wire from positive side of battery to o/w side of ignition coil and it ran fine. Found too much voltage drop to coil because of bad side stand relay.

Title: Re: Engine Missfire at High Revs
Post by stuartross109 on 05/25/07 at 12:24:59

Thanks for all your suggestions. I don't think its plug related as I have just fitted a new one and it has a good spark but it is worth a try. I will try the suggestion with the wire.

Having had a look at previous messages I looked at my cam chain tensioner and it was about to go (27000 mls). It gave no real tension to the chain so I wonder if this is part of the problem.

I will try the suggested mod. Will keep you posted.

This is probably covered elsewhere but can I replace the chain without taking the head off?

Thanks

Title: Re: Engine Missfire at High Revs
Post by verslagen1 on 05/25/07 at 12:37:38

No, replacing the chain can't be replaced thru the head.

All you need to do is remove the clutch cover and check the tensioner projection. More than 18mm from the housing to the shoulder and it's time to be worked on.

If it does, you'll need to remove the head cover. Optional at your discretion is the welded tab slavy mod. Check out the cam chain library in the tech section. But I would recommend measuring the chain stretch before you decide which way you go.

Title: Re: Engine Missfire at High Revs
Post by justin_o_guy on 05/25/07 at 14:49:15

Did you put that new plug in after this started? Just before? If it started just after the new plug, be aware, new doesnt mean good.

Title: Re: Engine Missfire at High Revs
Post by stuartross109 on 06/28/07 at 13:17:43

Have tried new plug and re-cleaned the carb. Model does not have side stand relay.
On reflection the missfire is not so much at high revs as wide throttle openings. The bike will rev well as long as it takes its time on up ro 3/4 throttle opening. Open it wide and it starts to missfire straingh away. Back off and it stops. Seems carb related but the thing is clean and sound. I would have thought wrong size main jet but ran fine previously.
Any other thoughts?
Stu

Title: Re: Engine Missfire at High Revs
Post by Savage_Rob on 06/28/07 at 13:47:24

Check for exhaust leaks. If one of your exhaust gaskets is leaking, it can allow air to be sucked into the exhaust stream and cause postignition of unburnt fuel.

Title: Re: Engine Missfire at High Revs
Post by LANCER on 06/29/07 at 08:23:33

Are you checking the plug for an overly rich condition?

Title: Re: Engine Missfire at High Revs
Post by stuartross109 on 06/30/07 at 10:04:22

Hi
Does look quite rich. Any thoughts as to possible causes?
Stu

Title: Re: Engine Missfire at High Revs
Post by barry68v10 on 06/30/07 at 11:13:05

As soon as I read this thread, my first thought was too big main jet...do you know what's in it?

Title: Re: Engine Missfire at High Revs
Post by serowbot on 06/30/07 at 11:48:23

Check for fuel in the carb's vac line. Probably not the problem but, it's so easy to rule out. Any gas at all in there and that's your problem.
Also make sure the line is fitting the nipples securely.
Next I'd look for a sticky slide. You check that by removing the four screws from the top of the carb. Carefull they tend to strip out. Replace them with allen heads, if you go there.

Title: Re: Engine Missfire at High Revs
Post by stuartross109 on 06/30/07 at 12:14:39

Thanks

I think the main jet is 155 (only because that whats in the manual though). Did run fine previously.

I have checked the slide and its free running.

?????
Stu

Title: Re: Engine Missfire at High Revs
Post by barry68v10 on 06/30/07 at 16:56:55

When you say it ran fine previously, does that mean at the same temps?

Title: Re: Engine Missfire at High Revs
Post by stuartross109 on 07/01/07 at 00:04:21

Yes
In the same conditions its been fine for years.
Stu